In the case of a data-carrying core, such as telephone or computer lines, it is important to provide security from wire tapping or eavesdropping on confidential information carried by the core, and to protect data lines used for electronic transfer of money between financial institutions. This it is necessary not only to stop information being extracted but also to stop erroneous information being added or current information being changed.
There is also a need for detecting imminient failure of a core which is fundamental to the safety or operation of a control system such as an aircraft hydraulic system or a missle fire control system.